Within the field of dentistry, a variety of materials are used to replace or assist in replacing missing tooth structure, including restorative materials and bonding agents (often referred to as adhesives). A restorative material typically replaces a portion of the tooth structure, whereas a bonding agent acts as a bond between the tooth structure and the restorative material. Due to their different uses, restorative materials and bonding agents may have different properties and qualities. For example, bonding agents need to have sufficient fluidity and often require the presence of a solvent such as water, acetone or alcohol to be effective. Typically, bonding agents lack filler materials or have filler levels less than 5% by weight. As such, bonding agents lack sufficient strength or aesthetics to be used as restorative materials in situations which require larger restorative quantities. Restorative materials need to have physical properties such as high compressive strength and low wear, and preferably have an acceptable aesthetic appearance, e.g., tooth-like appearance.
One type of dental material includes resin-reinforced glass ionomers. Glass ionomers require water for all or part of their curing or setting mechanism and require the mixing of two or more ingredients immediately prior to use. However, their uptake of water during setting, their subsequent expansion or contraction and their generally poor overall performance in terms of esthetic appearance have limited the use of glass ionomers as restorative materials. See, e.g., U.S. Pat. No. 5,264,513 to Kunio.
Another type of bonding agent or adhesive includes dental materials containing acidic monomers. Acidic monomers are polymerizable compounds that contain acid groups such as phosphoric, phosphonic, phosphinic, sulfuric, sulfonic or sulfinic moieties. Acidic monomers, such as phosphate esters, are known. Buonocore discussed such materials as early as 1956 in J. Dent. Res., 1956, pp. 846-851. In addition, solvent based materials containing phosphate esters were described in Adhesive Restorative Dental Materials, 1961, pp. 195-198. Typically, these materials contain high levels of volatile solvents and contain little or no inorganic filler material. See, e.g., U.S. Pat. No. 5,089,051 to Eppinger et al. and U.S. Pat. No. 6,245,872 to Frey et al. Generally, acidic monomers have not been previously used in combinations greater than 40% by weight due to the difficulty in polymerizing acidic monomers in high concentrations and/or the diminished physical properties obtained. See, e.g., U.S. Pat. No. 5,733,949 to Imazato et al.
A category of dental restorative materials includes resin-based composite materials. These composite materials typically contain both reactive monomers and non-reactive fillers. They are also typically hydrophobic in nature and do not bond well to tooth structure. A tooth itself may contain between 5-20% water and is present in an aqueous oral environment. Ion releasing resin-based restorative materials, including non-acidic monomers, are described in U.S. Pat. No. 6,180,688 to Rheinberger et al.